Shared active pixel sensor

ABSTRACT

A shared active pixel sensor includes a first shared photodiode, a first shared sense node, a first transfer gate, a first shared reset gate and a first shared source follower gate. The first shared photodiode consists of a first signal node and a second signal node. The first shared sense node is electrically connected to the first shared photodiode. The first transfer gate is disposed between the first signal node and the first shared sense node so that the first signal node and the first shared sense node together serve as a source and a drain controlled by the first transfer gate. The first shared reset gate is electrically connected to the first shared sense node. The first shared source follower gate is capable of reading a photocurrent from the first shared photodiode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims the benefitof U.S. patent application Ser. No. 14/201,913, filed on Mar. 9, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a shared active pixel sensor(APS). In particular, the present invention is directed to a sharedactive pixel sensor so that a single multi-share pixel unit can serve asmultiple pixels.

2. Description of the Prior Art

A photodiode is a semiconductor device for use as an image sensor.Basically speaking, to make an image sensor more sensitive, it is a goodidea for a photodiode to occupy an area as large as possible so regionsother than the photodiode region in each pixel should be minimized. Forthe sake of saving more pixel area, pixels are always designed to shareread out circuits with other neighboring pixels.

In terms of the number of sharing pixels, there are various sharingpixels, for example a 2-share or a 4-share pixel. Generally speaking, areset transistor or a source follower is the first candidacy. Otherwise,it is only one option available to reduce the STI (shallow trenchisolation) area or the floating diffusion area to achieve a highconversion gain or high sensing area.

Accordingly, another novel pixel structure is still needed forminimizing the pixel area.

SUMMARY OF THE INVENTION

The present invention proposes a new shared active pixel sensorstructure for minimizing the pixel area. The combined photodiode orreducing the transistor numbers is another possible solution of thepresent invention.

The present invention proposes a shared active pixel sensor. The newshared active pixel sensor includes a first shared photodiode, a firstshared sense node, a first transfer gate, a first shared reset gate anda first shared source follower gate. The first shared photodiodeconsists of a first signal node and a second signal node. The firstshared sense node is electrically connected to the first sharedphotodiode. The first transfer gate is disposed between the first signalnode and the first shared sense node so that the first signal node andthe first shared sense node together serve as a source and a draincontrolled by the first transfer gate. The first shared reset gate iselectrically connected to the first shared sense node. The first sharedsource follower gate is capable of reading a photocurrent from the firstshared photodiode.

In one embodiment of the present invention, the first signal node andthe second signal node are respectively disposed at different corners ofthe first shared photodiode.

In another embodiment of the present invention, only one of the firstsignal node and the second signal node is switched on at one time.

In another embodiment of the present invention, the first shared resetgate, the first shared source follower gate and the first transfer gateoperate sequentially to control the first signal node and the firstshared sense node.

In another embodiment of the present invention, the shared active pixelsensor further includes a second shared photodiode, a third transfergate and a second shared source follower gate. The second sharedphotodiode includes a third signal node electrically connected to thefirst shared sense node. The third transfer gate is disposed between thethird signal node and the first shared sense node so that the thirdsignal node and the first shared sense node together serve as a sourceand drain pair controlled by the third transfer gate. The second sharedsource follower gate is capable of reading a photocurrent from thesecond shared photodiode.

In another embodiment of the present invention, the first shared resetgate is disposed between the second shared source follower gate and thefirst shared source follower gate.

In another embodiment of the present invention, the first shared sensenode is electrically connected to two transfer gates of different sharedphotodiodes.

In another embodiment of the present invention, the shared active pixelsensor independently operates as two pixels by means of the first signalnode and the second signal node.

The present invention proposes another shared active pixel sensor (APS).The new shared active pixel sensor includes a first shared photodiode, afirst shared sense node, a first transfer gate, a first shared resetgate and a first shared source follower gate. The first sharedphotodiode includes at least a first signal node and a second signalnode. The first shared sense node is electrically connected to the firstshared photodiode. The first transfer gate is disposed between the firstsignal node and the first shared sense node so that the first signalnode and the first shared sense node together serve as a source and adrain which are controlled by the first transfer gate. The first sharedreset gate is electrically connected to the first shared sense node. Thefirst shared source follower gate reads a photocurrent from the firstshared photodiode.

In one embodiment of the present invention, the first signal node andthe second signal node are respectively disposed at different corners ofthe first shared photodiode.

In another embodiment of the present invention, the first sharedphotodiode further includes a third signal node and a fourth signalnode.

In another embodiment of the present invention, only one of the firstsignal node, the second signal node, the third signal node and thefourth signal node is switched on at one time.

In another embodiment of the present invention, the first shared resetgate, the first shared source follower gate and the first transfer gateoperate sequentially to control the first signal node and the firstshared sense node.

In another embodiment of the present invention, the shared active pixelsensor further includes a second shared photodiode, a fifth transfergate and a second shared source follower gate. The second sharedphotodiode includes a fifth signal node electrically connected to thefirst shared sense node. The fifth transfer gate is disposed between thefifth signal node and the first shared sense node so that the fifthsignal node and the first shared sense node together serve as a sourceand drain pair controlled by the fifth transfer gate. The second sharedsource follower gate to read a photocurrent from the second sharedphotodiode.

In another embodiment of the present invention, the first shared sensenode is disposed between the second shared source follower gate and thefirst shared source follower gate.

In another embodiment of the present invention, the first shared sensenode is electrically connected to at most four transfer gates ofdifferent shared photodiodes.

In another embodiment of the present invention, the first shared resetgate is disposed between the first shared photodiode and the secondshared photodiode.

In another embodiment of the present invention, the shared active pixelsensor further includes a second shared sense node, a second sharedreset gate, a third shared source follower gate and a forth sharedsource follower gate. The second shared sense node is electricallyconnected to the second signal node, and controlled by a second transfergate of the first shared photodiode. The second transfer gate isdisposed between the second signal node and the second shared sensenode. The second shared sense node is electrically connected to a sixthsignal node of the second photodiode and controlled by a sixth transfergate of the second shared photodiode. The sixth transfer gate isdisposed between the sixth signal node and the second shared sense node.The second shared reset gate is electrically connected to the secondshared sense node. The third shared source follower gate is disposedadjacent to the second transfer gate to read a photocurrent from thefirst shared photodiode. The forth shared source follower gate isdisposed adjacent to the sixth transfer gate to read a photocurrent fromthe second shared photodiode.

In another embodiment of the present invention, the shared active pixelsensor independently operates as four pixels by means of the firstsignal node, the second signal node, the third signal node and thefourth signal node.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of the four-shared active pixel sensorlayout structures in accordance with the present invention.

FIG. 2 illustrates one embodiment of the two-shared active pixel sensorlayout structures in accordance with the present invention.

DETAILED DESCRIPTION

For minimizing the pixel area of a photodiode, the present inventionprovides a novel shared active pixel sensor. In the novel shared activepixel sensor, there are various shared elements which are shared by theadjacent pixel sensors to minimize the area occupied by element regionsother than the photodiode region.

As used herein, terms including an ordinal such as “a first” or “asecond” and the like may be used to explain various constitutionalelements, but the constitutional elements are not limited thereto. Theterms are used only to distinguish one constitutional element fromanother constitutional element. For example, a first constitutionalelement may be named as a second constitutional element, and similarly,a second constitutional element may be named as a first constitutionalelement, without departing from the right scope of the invention.

Please refer to FIG. 1 or FIG. 2. FIG. 1 and FIG. 2 respectivelyillustrate two possible shared active pixel sensor layout structures inaccordance with the gist of the present invention. In FIG. 1, the sharedactive pixel sensor 100 of the present invention includes a first sharedimage sensor 111, a first shared sense node 121, a first transfer gate131, a first shared reset gate 141 and a first shared source followergate 151. In FIG. 2, the shared active pixel sensor 200 of the presentinvention includes a first shared image sensor 211, a first shared sensenode 221, a first transfer gate 231, a first shared reset gate 241 and afirst shared source follower gate 251.

The shared active pixel sensor of the present invention is amulti-shared photodiode with respect to the neighboring photodiode s. Inother words, the multi-shared active photodiode is at least a two-sharedimage sensor 201 as shown in FIG. 2 or a four-shared image sensor 111 asshown in FIG. 1. For example, in FIG. 1, there are four four-sharedimage sensors, namely 111, 112, 113 and 114, illustrated in the sharedactive pixel sensor 100, and in FIG. 2, there are two two-shared imagesensors, namely 211 and 212, illustrated in the shared active pixelsensor 200. Each shared image sensor in either FIG. 1 or FIG. 2 sharessome elements with neighboring image sensors. In the followingdescriptions, the shared image sensors 111 and 211 are taken asexemplary shared active pixels.

Each shared image sensor includes at least two signal nodes, namely afirst signal node and a second signal node. As shown in FIG. 1, imagesensors are illustrated and the exemplary shared image sensor 111 whichhas a first signal node 101, a second signal node 102, a third signalnode 103 and a fourth signal node 104 serves as a four-shared activephotodiode.

Similarly as shown in FIG. 2, the photodiode 211 only needs a firstsignal node 201 and a second signal node 202. In other words, thephotodiode 211 consists of a first signal node 201 and a second signalnode 202 to serve as a two-shared photodiode.

In one embodiment of the present invention, each signal node is disposedat one corner of the image sensor so multiple signal nodes arerespectively disposed at different corners in the same photodiode. Forexample, as shown in FIG. 2, the first signal node 201 and the secondsignal node 202 are respectively disposed at two different corners ofthe first shared image sensor 211. Or as shown in FIG. 1, the firstsignal node 101, the second signal node 102, the third signal node 103and the fourth signal node 104 are respectively disposed at fourdifferent corners of the first shared image sensor 111.

As shown in FIG. 1, the first shared sense node 121 is disposed adjacentto and electrically connected to the first shared photodiode 111.Further, the first shared sense node 121 is disposed at a signal path105 half way between the first shared image sensor 111 and the firstshared reset gate 141. The first shared reset gate 141 is electricallyconnected to the first shared sense node 121. Similarly, as shown inFIG. 2, the first shared sense node 221 is disposed adjacent to andelectrically connected to the first shared image sensor 211. Also, theshared sense node is disposed at a signal path 205 half way between thefirst shared photodiode 211 and the first shared reset gate 241. Thefirst shared reset gate 241 is electrically connected to the firstshared sense node 221. Generally, a shared reset gate is in charge ofthe accumulation of a charge at one shared sense node in a sharedphotodiode. Moreover, a shared reset gate is disposed between twoadjacent shared source follower gates.

There are four transfer gates 131/132/133/134 illustrated in FIG. 1.Each transfer gate is disposed between a signal node and a shared sensenode. For example, the first transfer gate 131 is disposed between thefirst signal node 101 and the first shared sense node 121 so that thefirst signal node 101 and the first shared sense node 121 together serveas a source and a drain which are controlled by the first transfer gate131. Other transfer gate 132, 133 or 134 functions in a similar way.

There are four transfer gates 231/232/233/234 illustrated in FIG. 2.Each transfer gate is disposed between a signal node and a shared sensenode. For example, the first transfer gate 231 is disposed between thefirst signal node 201 and the first shared sense node 221 so that thefirst signal node 201 and the first shared sense node 121 together serveas a source and a drain which are controlled by the first transfer gate231. Other transfer gate 232, 233 or 234 functions in a similar way.

For example, the charge accumulating in a shared photodiode (the sharedimage sensor 111 or 211) flows from a given signal node (source) towardsa given shared sense node (drain) which are controlled by a specifictransfer gate so the transfer gate is in charge of the charge transferfrom the given signal node (source) towards the given shared sense node(drain).

Further, as shown in FIG. 1, the first shared source follower gate 151is used to read a photocurrent from the first shared image sensor 111.Similarly, as shown in FIG. 2, the first shared source follower gate 251is used to read a photocurrent from the first shared image sensor 211.Generally speaking, the function of a shared source follower gate is toread a photo-signal coming from a shared reset gate and is in charge ofconverting the photo-signal into a voltage signal.

In one embodiment of the present invention, a shared reset gate, thecorresponding shared source follower gate and the corresponding transfergate operate sequentially to control the signal node and the sharedsense node. This helps to optimize the operation and the efficiency of agiven shared active pixel sensor.

In either a two-shared photodiode or a four-shared photodiode, theshared photodiode has more than one signal node. When more than onesignal node is in a “switched on” state, it is not advantageous todetect the photocurrent. Accordingly, in one embodiment of the presentinvention, only one of the signal nodes in a shared active pixel sensoris switched on at one time to guide the photocurrent to be collected. Inanother embodiment of the present invention, a shared image sensor mayindependently operate as if there were multiple pixels present by meansof the first signal node and the second signal node. For example, theshared image sensor 111 may independently operate like four pixels whenthe first signal node 101, the second signal node 102, the third signalnode 103 or the fourth signal node 104 is switched on at one time tooutput the photocurrent to four differently oriented transfer gates131/132/133/134 because there are four second signal nodes available.

Because the present invention provides a multi-shared image sensor, anysingle multi-shared image sensor is surely electrically connected to oneor more adjacent multi-shared image sensors by means of a sharedelement. In one embodiment of the present invention, as shown in FIG. 1or in FIG. 2, the shared active pixel sensor 100 further includes asecond shared image sensor 112, an optional third shared image sensor113 and an optional fourth shared image sensor 114. Similarly, as shownin FIG. 2, the shared active pixel sensor 200 further includes a secondshared image sensor 212 and an optional third shared image sensor 213.In another embodiment of the present invention, as shown in FIG. 1 or inFIG. 2, the first shared sense node 121/221 is electrically connected totwo transfer gates 131/135 or 231/233 of different shared image sensors111/112 or 211/212.

Each additional shared image sensor or each optional shared image sensorhas similar structures and functions like the first shared image sensor111 or 211 as described above. For example, in FIG. 1 there are foursignal nodes 105/106/107/108, a second shared sense node 122, fourtransfer gates 135/136/137/138, a second shared reset gate 142 and asecond shared source follower gate 152 which correspond to the secondshared image sensor 112. Similarly, in FIG. 2, there are two signalnodes 203/204, a second shared sense node 222, two transfer gates233/234, a second shared reset gate 242 and a second shared sourcefollower gate 252 which correspond to the second shared image sensor212. Optionally, more optional signal nodes, shared sense nodes,transfer gates, shared reset gates and shared source follower gates arepossible.

As shown in FIG. 1, the second shared image sensor 112, the third sharedimage sensor 113 and the fourth shared image sensor 114 are respectivelydisposed next to and electrically connected to the previously describedfirst shared image sensor 111. The first shared image sensor 111, thesecond shared image sensor 112, the third shared image sensor 113 andthe fourth shared image sensor 114 share various elements which aredirectly connected to them.

Take one of the second shared image sensor 112, the third shared imagesensor 113 and the fourth shared image sensor 114 for example, thesecond shared image sensor 112 includes a fifth signal node 105electrically connected to the first signal node 101 via the first sharedsense node 121. The fifth transfer gate 135 is disposed between thefifth signal node 105 and the first shared sense node 121 so that thefifth signal node 105 and the first shared sense node 121 together serveas a source and drain pair controlled by the fifth transfer gate 135.

Similarly, as shown in FIG. 2, the second shared photodiode 212 includesa third signal node 203 electrically connected to the first signal node201 via the first shared sense node 221. The third transfer gate 233 isdisposed between the third signal node 203 and the first shared sensenode 221 so that the third signal node 203 and the first shared sensenode 221 together serve as a source and drain pair controlled by thethird transfer gate 233. Other elements work in a similar way.

As shown in FIG. 1, the second shared source follower gate 152 is usedto read a photocurrent from the second shared image sensor 112.Similarly, as shown in FIG. 2, the second shared source follower gate252 is used to read a photocurrent from the second shared image sensor212. Generally speaking, the function of a shared source follower gateis to read a photo-signal coming from a shared reset gate and is incharge of converting the photo-signal into a voltage signal.

In view of the above, the present application provides multiple layoutsof a multi-share pixel sensor structures. In one aspect, the layouts mayminimize the pixel area. In a second aspect, the numbers of thetransistors can be reduced. Further, a single multi-share pixel unit mayserve as multiple pixels.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A shared active pixel sensor (APS), comprising: afirst shared photodiode consisting of a first signal node and a secondsignal node; a first shared sense node electrically connected to saidfirst shared photodiode; a first transfer gate disposed between saidfirst signal node and said first shared sense node so that said firstsignal node and said first shared sense node together serve as a sourceand a drain controlled by said first transfer gate; a first shared resetgate electrically connected to said first shared sense node; a firstshared source follower gate to read a photocurrent from said firstshared photodiode; a second shared photodiode comprising a third signalnode electrically connected to said first shared sense node; a thirdtransfer gate disposed between said third signal node and said firstshared sense node so that said third signal node and said first sharedsense node together serve as a source and drain pair controlled by saidthird transfer gate; and a second shared source follower gate to read aphotocurrent from said second shared photodiode, wherein said firstshared reset gate is disposed between said second shared source followergate and said first shared source follower gate.
 2. The shared activepixel sensor of claim 1, wherein said first signal node and said secondsignal node are respectively disposed at different corners of said firstshared photodiode.
 3. The shared active pixel sensor of claim 1, whereinonly one of said first signal node and said second signal node isswitched on at one time.
 4. The shared active pixel sensor of claim 1,wherein said first shared reset gate, said first shared source followergate and said first transfer gate operate sequentially to control saidfirst signal node and said first shared sense node.
 5. The shared activepixel sensor of claim 1, wherein said first shared sense node iselectrically connected to two transfer gates of different sharedphotodiodes.
 6. The shared active pixel sensor of claim 1 independentlyoperated as two pixels by means of said first signal node and saidsecond signal node.